This randomized, double-blind and placebo-controlled dose titration trial is planned to enroll up to 30 healthy adult volunteers, and will evaluate the safety, tolerability and pharmacokinetics of multiple-ascending doses of APD811 and the optimal titration schedule. Arena previously evaluated single-ascending doses of APD811 in the initial Phase 1 clinical trial.

"Treatment with prostacyclin receptor agonists is considered standard of care for advanced PAH, but approved drugs in this class require intravenous, subcutaneous or inhaled delivery methods," said William R. Shanahan, M.D., Arena's Senior Vice President and Chief Medical Officer. "APD811 has the potential to improve treatment for this life-threatening disorder by providing patients with an oral, once-daily option targeting the prostacyclin receptor. This drug candidate was discovered internally by our scientists as part of our effort to bring best-in-class treatments to patients."

AboutPulmonary Arterial Hypertension (PAH)

PAH is a progressive, life-threatening disorder characterized by increased pressure in the arteries that carry blood from the heart to the lungs. The increased pressure strains the heart, which can limit physical activity, result in heart failure and reduce life expectancy. Based on data from the Registry to EValuate Early And Long-term PAH disease management (REVEAL) of patients in the United States, there is an estimated five-year survival rate of 57% from diagnosis.

AboutAPD811

APD811, an orally available agonist of the prostacyclin (IP) receptor, is an investigational drug candidate discovered by Arena and intended for the treatment of PAH. Treatment with IP agonists, which can slow disease progression and improve exercise tolerance in PAH patients, is considered standard of care for advanced PAH. Currently available IP agonists belong to the prostanoid class of molecules, and these products need to be administered frequently or continuously through intravenous, subcutaneous or inhaled delivery methods. Arena believes that an orally available, non-prostanoid IP agonist that provides clinical benefits similar to currently available IP agonists has the potential to improve the standard of care for PAH.

About Arena Pharmaceuticals

Arena Pharmaceuticals is a biopharmaceutical company focused on discovering, developing and commercializing novel drugs for weight management, cardiovascular disease, inflammation and other disorders. Arena's US operations are located in San Diego, California, and its operations outside of the United States, including its commercial manufacturing facility, are located in Zofingen, Switzerland. For more information about Arena, please visit www.arenapharm.com.

Arena Pharmaceuticals® and Arena® are registered service marks of Arena Pharmaceuticals, Inc.

Forward-Looking Statements

Certain statements in this press release are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include statements about the advancement, therapeutic indication and use, safety, efficacy, tolerability and mechanism of action of APD811; the protocol, design, scope, enrollment, potential results and other aspects of the Phase 1 multiple dose clinical trial of APD811; the potential of APD811 and orally available, non-prostanoid IP agonists in general; Arena's effort to bring treatments to patients; and Arena's efforts, focus, goals, strategy, research and development programs, and ability to discover and develop compounds and commercialize drugs. For such statements, Arena claims the protection of the Private Securities Litigation Reform Act of 1995. Actual events or results may differ materially from Arena's expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, but are not limited to, the following: APD811 may not have an adequate safety margin or otherwise be sufficient for further development or regulatory review or approval; risks related to commercializing drugs, including regulatory, manufacturing and supply issues and the pace of market acceptance; cash and revenues generated from lorcaserin, including the timing and impact of competition; the timing and outcome of regulatory review is uncertain; government and commercial reimbursement and pricing decisions; risks related to relying on collaborative agreements; the timing and receipt of payments and fees, if any, from collaborators; the entry into or modification or termination of collaborative arrangements; unexpected or unfavorable new data; nonclinical and clinical data is voluminous and detailed, and regulatory agencies may interpret or weigh the importance of data differently and reach different conclusions than Arena, request additional information, have additional recommendations or change their guidance or requirements before or after approval; data and other information related to any of Arena's research and development programs may not meet safety, efficacy or other regulatory requirements or otherwise be sufficient for regulatory review, approval or continued marketing; Arena's ability to obtain and defend patents; the timing, success and cost of Arena's research and development programs; results of clinical trials and other studies are subject to different interpretations and may not be predictive of future results; clinical trials and other studies may not proceed at the time or in the manner expected or at all; having adequate funds; and satisfactory resolution of litigation or other disagreements with others. Additional factors that could cause actual results to differ materially from those stated or implied by Arena's forward-looking statements are disclosed in Arena's filings with the Securities and Exchange Commission. These forward-looking statements represent Arena's judgment as of the time of this release. Arena disclaims any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.